The skin is the body's largest organ and serves as the primary protective barrier to the outside world. Any physical disruption (i.e., wound) to this organ must therefore be quickly and efficiently repaired in order to restore tissue integrity and function. Quite often proper wound healing is impaired with devastating consequences such as severe morbidity, amputations, or death. In humans and animals, protection from mechanical injury, chemical hazards, and bacterial invasion is provided by the skin because the epidermis is relatively thick and covered with keratin. Secretions from sebaceous glands and sweat glands also benefit this protective barrier. In the event of an injury that damages the skin's protective barrier, the body triggers a wound healing cascade of events.
The classical model of wound healing is divided into three or four sequential, yet overlapping, phases: (1) hemostasis, (2) inflammatory, (3) proliferative and (4) remodeling. The hemostasis phase involves platelets (thomboctytes) to form a fibrin clot to control active bleeding. The inflammatory phase involves migration of phagocytes to the wound to kill microorganisms and release of subsequent signaling factors to involve the migration and division of cells involved in the proliferative phase. The proliferative phase involves vascular cell production for angiogenesis, fibroblast cells to excrete collagen and fibronectin to form an extracellular matrix, and epithelial cells to reform the external epidermis. In addition, the wound is made smaller by myofibroblasts. Finally, collagen is remodeled and cells that are no longer needed are removed by programmed cell death (i.e., apoptosis).
The process of wound healing can be divided into two major phases: early phase and cellular phase. See FIG. 1. The early phase involves hemostasis which involves vasoconstriction, temporary blockage of a break by a platelet plug, and blood coagulation, or formation of a clot that seals the hole until tissues are repaired. The early phase also involves the generation of stimuli to attract the cellular responses needed to instigate inflammation. In the inflammation phase (see FIG. 2), white blood cells, or leukocytes, are attracted to the wound site by platelet-derived growth factor (PDGF), and these cells of the immune system are involved in defending the body against both infectious disease and foreign materials. There are 18 other known proteins involved in the inflammatory phase which interact to regulate this response. For example, IL-4, IL-10, and IL-13 are potent activators of B lymphocytes. However, IL-4, IL-10, and IL-13 are also potent anti-inflammatory agents. The phagocytic cells engulf and then digest cellular debris and pathogens and stimulate lymphocytes and other immune cells to respond to the wound area. Once the invading microorganisms have been brought under control, the skin proceeds through the proliferative and remodeling stage by a complex cascade of biochemical events orchestrated to repair the damage. This involves the formation of a scab within several hours. The scab temporarily restores the integrity of the epidermis and restricts the entry of microorganisms. After the scab is formed, cells of the stratum basale begin to divide by mitosis and migrate to the edges of the scab. A week after the injury, the edges of the wound are pulled together by contraction. Contraction is an important part of the healing process when damage has been extensive, and involves shrinking in size of underlying contractile connective tissue, which brings the wound margins toward one another. In a major injury, if epithelial cell migration and tissue contraction cannot cover the wound, suturing the edges of the injured skin together, or even replacement of lost skin with skin grafts, may be required to restore the skin. Interruption of this healing process by a breakdown in any of these wound healing processes will lead to a chronic wound.
Other skin wounds involve burns. Major burns are relatively common injuries that require multidisciplinary treatment for patient survival and recovery. More than 30,000 people the each year worldwide because of fire-related burn injuries. Many more are seriously injured, disabled, or disfigured because of all types of burns. There have been significant advances in medical care for burns over the last 15 years due to fluid resuscitation, wound cleaning, skin replacement, infection control, and nutritional support. These changes have primarily resulted from the use of early burn wound excursion, early adequate nutrition, and the use of surgical techniques that minimize blood and heat loss. Since modern treatment of burns has greatly advanced, sepsis has become the leading cause of death after a burn injury. Multiple antibiotic resistant bacteria and fungus now account for the bulk of deaths due to sepsis in burns, the etiology of which is due to antibiotic resistant bacteria and biofilm formation in the wound and extraneous nosocomial infections.
Impediments to wound healing include hypoxia, infection, presence of debris and necrotic tissue, use of inflammatory medications, a diet deficient in vitamins or minerals or general nutrition, tumors, environmental factors, and metabolic disorders such as diabetes mellitus. The primary impediments to acute wound healing are hypoxia, infection, wound debris, and anti-inflammatory medications. The molecular events in the wound healing process of acute, chronic and burn wounds continues to be studied and exhibits an extremely complex array of biochemical events imposing a regulated cascade of inter and intra cellular events. A rapidly growing field of wound healing research is centered around cellular growth factors and the use of these factors for the treatment of wounds. The biochemical response at the cellular level is a process involving intricate interactions among different cell functions which include energy production, structural proteins, growth factors, and proteinases. The treatment of wounds with known cellular growth factors has the potential ability to help heal wounds by stimulating the cellular processes involved in angiogenesis, cellular proliferation, regulating the production and degradation of the extracellular matrix, and being the signal for attracting the inflammatory cells and fibroblasts. Obviously, this complexity requires a plethora of biochemical reactions to provide the functions necessary to accomplish healing of the wound and is not completely understood at this point.
One emerging area of research is the metabolic effect of the alpha keto acids on wound healing. U.S. Pat. No. 6,329,343 discloses the use of a composition of salts of pyruvic acid and/or salts of pyruvic acid and alpha keto glutaric acid, a mixture of fatty acids, and an effective amount of an antibacterial agent as a bioadhesive antibacterial wound healing composition.
Several strategies have been employed to combat the significant infectious complication rates associated with wounds. However, to-date, these strategies have been mainly limited to improved surgical asepsis, surgical technique, and administrative regimens of peri-operative systemic antibiotics and local antibiotic irrigation procedures which have not been well defined. New approaches are emerging in the clinic, including vacuum-sealed dressings, transparent film dressings, irrigation with antimicrobial agents, use of the port and cap, use of new agents such as deuteroporphyrin, gamma interferon (IFN-γ), silver sulfadiazone water soluble gel, geomagnetic therapy, and natural remedies such as milliacynic oil and lysozyme. Unfortunately, few of these innovations have made a major impact on infection and fatality rates and have been shown to have cellular toxicity issues. Most new approaches involve delivery of antimicrobial compounds, to which many wound pathogens are resistant, in some form of salve or in dressings. These treatments lend themselves to continued production of antibiotic resistant bacteria which will negatively affect future therapies against resistive bacteria such as Methicillin-Resistant Staphylococcus aureus (MRSA), Vancomycin-resistant enterococci (VRE) and Acinetobacter baumanni. A baumannii accounts for 6% of Gram-negative infections in intensive care facilities in the USA, with mortality rates as high as 54% having been reported. Isolation of MDR Acinetobacter soared from 6.7% in 1993 to 29.9% by 2004, emphasizing the need for newer and better drugs. Out of 1,040 antibiotics tested only 20 (1.92%) exhibited significant antimicrobial activity and only five compounds exhibited activity against the more resistant BAA-1605 A. baumanni. Today, MRSA and C. difficile are the leading causes of nosocomial infection in most parts of the world. In 2003, S. aureus was the leading pathogen associated with skin and soft tissue infections. In the last 20 years, MRSA has moved from an exclusively hospital-acquired pathogen (HA-MRSA) to another type known as a community-acquired pathogen, CA-MRSA. In fact, it has been stated that topical application of antibiotic solutions for lower-limb open fracture wounds offers no advantage over the use of a non sterile soap and may increase the risk of wound-healing problems.
Wound healing and “good” care of wounds has been synonymous with topical prevention and management of microbial contamination. Today's primary therapy involves the use of either topical application of antiseptics or systemic and topical use of antibiotics. The general perspective is that topical application of antibiotics to wounds has no advantages over the use of other antiseptic methods and may increase the risk of wound-healing by producing a sovereign bacteria that is resistant within the wound. The use of silver-based dressings for therapy against infections are widely used in chronic wound and burn therapy. There are several of these commercially available such as Acticoatt™, Aquacels Age®, Contreet® Foam, PolyMem® Silver, Urgotul® SSD). These silver containing dressings do not kill spores or biofilms and require long exposure times that may become cytotoxic over time. The major cause of sepsis in burn wounds, Aspergillus niger has a 70% fatality and is not susceptible to silver compounds.
The cytotoxic effect would explain, in part, the clinical observation of delayed wound healing or inhibition of wound epithelialization after the use of certain topical silver dressings.
There are a myriad of solutions available that claim to kill 99.9% of MRSA and other vegetative bacteria and some spores on surfaces and skin (e.g., hand sanitizers). Therefore, these solutions leave one viable bacterium, or spore, in a thousand or a thousand viable bacteria, or spores, in a million after treatment. However, contaminated surfaces can contain millions of bacteria, some of which can be contained within complex matrices such as blood drops, thus making them difficult to kill. Other types of bacteria, such as Bacillus subtilis, form biofilms on surfaces of endoscopes and other medical devices for insertion into the body, which affects the kill efficacy of most disinfectants. These low level disinfectants, often called sanitizers, that claim to kill 99.9% of the bacteria present will not completely kill all bacteria which are present in higher populations (colonized), contained within a complex matrix, or existing as a biofilm.
There are currently several topical antiseptics on the market that are used to diminish the growth of bacterial infections in wounds. Most antiseptics are not suitable for open wounds because they may impede wound healing by direct cytotoxic effects to keratinocytes and fibroblasts. In general, current topical antiseptics have limited bactericidal effect (e.g., 3 log reduction in 30 minute exposure) and nearly all have some cytotoxicity effect which varies with concentration and application time.
There are primarily five high level disinfectants/sterilants in use today. These include glutaraldehyde, orthopthalaldehyde, hypochlorite, hydrogen peroxide, and peracetic acid. The aldehydes are highly toxic and take a very long time to affect a >99.9999% (or 6 log kill). The most successful high level disinfectants used today are oxidizers such as hypochlorites, hydrogen peroxide and peracetic acid. The reactive advantage for disinfection by oxidation is the non-specific free radical damage to all components of the microbe, including proteins, lipids, and DNA. Therefore, microbial resistance to oxidation at high enough solution concentration is virtually non-existent. Safe and non-toxic concentrations of hydrogen peroxide are not capable of killing spores or high populations of microbes. Hypochlorous acid, which is formed by PMN by myeloperoxidase-mediated peroxidation of chloride ions, is easily neutralized at physiological pH by nitrite, a major end-product of cellular nitric oxide (NO) metabolism, and its bactericidal effects subsequently diminished and it is not as effective as silver sulfadiazine, a common topical wound sanitizer. However, it appears that hypochlorous acid does not inhibit wound healing at the concentrations for the effective biocidal levels used. That may be because it is a natural compound found in the inflammatory phase of wound healing. Peracetic acid is used mainly in the food industry, where it is applied as a cleanser and as a disinfectant. Since the early 1950's, acetic acid was applied for bacteria and fungi removal from fruits and vegetables. It was also used for the disinfection of recycled rinsing water for foodstuffs. Nowadays peracetic acid is applied for the disinfection of medical supplies and to prevent biofilm formation in pulp industries. It can be applied during water purification as a disinfectant and for plumbing disinfection. Peracetic acid is produced by a reaction between hydrogen peroxide and acetic acid or it can also be produced by oxidation of acethaldehyde. Peracetic acid is a very powerful oxidant; the oxidation potential outranges that of chlorine and chlorine dioxide. Peracetic acid has not been tested in wound healing. However, it is not known to be involved in any significant cellular metabolism and is typically produced with toxic sulfuric acid catalyst. Thus, many conventional topical wound sanitizers have various limitations.
As stated above, a drawback of the peroxyacid-based chemical disinfectants is their inherent lack of stability, which poses a challenge for shelf-life when used for long term applications. Thus, a need exists for a peracid-based disinfectant, which is an effective broad spectrum antimicrobial, is in an easily removable homogenous antimicrobial coating composition providing both short-term and extended long-term antimicrobial efficacy after application to a surface or a wound.
In addition, there is a continuing need for new topical wound sanitizers, healers or both, and in particular there is a need to develop peroxyacids that are effective sporocides, bactericids and virucides for wounds which are easy to handle and store. Moreover, there is a need for peroxyacids that are easy to handle and store and that have a low corrosive nature. It is therefore desirable to develop a sanitizer that does not decompose rapidly and violently and that can be used as a topical wound sanitizer or as an antimicrobial coating.
The present invention is directed toward overcoming one or more of the problems discussed above.